1. Field of the Invention
The present invention relates to an apparatus for adjusting B.D.C.position (bottom-dead-center position) of a slide in an apparatus for a mechanical press.
2. Description of the Related Art
In cases where a material is punched with a punch and a die, it is necessary to effect punching by maintaining an accurate bottom-dead-center position of a slide so as to prolong the life of the punch and the die. In cases where coining is effected in which a material is compressed by the punch and the die, or scoring is effected in which the material is marked with notches and incisions, an additional load due to the contacting of the slide against a stopper block occurs in a mechanical press in addition to a working load. Because of this, it is conducted to accurately control the penetration of the punch into the material and the thickness of a remaining portion of the material when the slide which has approached a bolster is brought into contact with the stopper block. When a press operation is started, the temperatures of members such as connecting rods which connect a crank shaft and the slide increase due to the motion, and such members undergo thermal expansion. Since the temperature rise is not uniform depending on the members, in the case of punching, the bottom-dead-center position of the slide is offset downward from an accurate position. Also, in the cases of coining and scoring, the additional load due to the stopper block increases, so that a large press load is generated during press working.
To overcome the above problem, a method in which temperature-controlled oil is applied to the connecting rods (Japanese Patent Application Publication No. 30569/1989), and the use of an adjusting screw mechanism for adjusting the die height are conventionally known.
With the conventional technique in which temperature-controlled oil is applied to the connecting rods, an apparatus for adjusting the oil temperature is required. It is very difficult to adjust the length of the connecting rods accurately by the temperature-controlled oil, thereby making it virtually difficult to obtain a predetermined bottom-dead-center position of the slide. With the conventional technique using the die-height adjusting screw mechanism, an adjustment screw for eliminating the looseness of the adjusting screw during a press operation must be locked with a lock nut, and during the die height adjustment, the die height adjustment must be made after the lock of the lock nut is released, and then the lock must be provided again by means of the lock nut. In the case of this die-height adjusting screw mechanism, if this die-height adjusting operation is carried out during the press operation, the bottom-dead-center position of the slide changes substantially due to the looseness of the adjusting screw while the lock is being released. As such, with the conventional techniques, the means for correcting the bottom-dead-center position of the slide, which changes due to the thermal expansion of the connecting rods and the like during a press operation, have not necessarily been effective.